Prior art recording materials are described below using a color proof as exemplary since almost the same description can be made with regard to other materials in the field except for their uses.
An overlay system is a typical example of a color proof system. In this system, different monochrome films are laminated to produce a multi-color image which has a poor image quality because it must be seen through films.
A surprint system is known as another type of color proof system in which a multi-color image is provided on a single sheet. In this system, a multicolor image is obtained by laminating images of different colors one by one on a single support. For example, Chromalin (Du Pont Co.), Match Print (3M), Color Art (Fuji Photo Film Co., Ltd.) and the like are known examples of this type of color proof system, but each of them requires four light-sensitive films for corresponding colors. This results in the generation of waste materials.
In addition, a color paper system is known as a process for the formation of a color image on a single light-sensitive sheet. In this system, a film original is superposed closely on a sheet of color paper, exposure is effected using different color filters and then a color image is obtained by wet development. Fine Checker (Fuji Photo Film Co., Ltd.), Consensus (Konica Corp.) and the like are known as examples of this type of system. However, since the color paper is sensitive to visible light, this system requires a darkroom or an exposure apparatus equipped with a darkroom, as well as the necessity to maintain a developing solution.
As a consequence, these prior art systems nave certain disadvantages such as the necessity of using a plurality of sheets, the generation of waste materials including transfer sheets and toners, difficulty in handing in daylight, necessity to establishing a developing system using developing solution and the like.
A process has been proposed solving these prior art problems. According to this process, an absolute dry system which does not generate any waste material is achieved by using: (a) a light-sensitive heat-sensitive recording material of the type in which a latent image is formed upon exposure in a photo-hardenable composition and, when heated, a component capable of undergoing color development or achromatization moves inside the light-sensitive heat-sensitive material in response to the latent image to form an image; and (b) a process for the preparation of color images which compresses exposing the light-sensitive heat-sensitive recording material through an image original, forming a latent image on the exposed portion by light-sensitive hardening and thereafter forming a visible image by heating the recording material to disperse the component capable of undergoing color development or achromatization remaining the un-hardened portion.
There are several illustrative examples of this type of recording material, and they are not only applicable to a recording system for a black-and-white image but also especially effective when used as a color recording material.
An illustrative example of this type of recording material is disclosed in JP-A 52-89915 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") in which two components of a two component type heat-sensitive recording material, for example, an electron accepting compound and an electron donating colorless dye, are separately arranged inside and outside or on both sides of microcapsules containing a photo-hardenable composition. In this recording material, however, the non-image portions are slightly colored thus showing a tendency for the contrast of the resulting image to be lowered, because development of color on the hardened portions cannot be prevented to a sufficient level even when the photo-hardenable composition in the microcapsules is hardened sufficiently.
A more preferred recording material which does not develop color in the non-image portions is disclosed, for instance, in JP-A-61-123838 in which a layer containing a photopolymerizable composition comprising an acid group-containing vinyl monomer and a photopolymerization initiator, an insulating layer and a layer comprising an electron donating colorless dye are laminated. In this type of recording material, thermal dispersion of the acid group becomes negligible in the non-image portion, i.e., in the hardened portion of the photopolymerizable layer. Although a color is not developed in the non-image portion because of such an effect, this recording material has the disadvantage of a somewhat low color density.
An example of a process for the formation of negative images in a similar manner is disclosed, for instance, in JP-A-60-119552 which comprises using a recording material in which a photopolymerizable composition comprising a monomer or a prepolymer capable of bleaching a dye and the dye to be bleached by the monomer or prepolymer are separately located. This recording material, however, has the same disadvantages as those of the above-described recording materials.
A recording material disclosed in Japanese Patent Application No. 1-224930 (corresponding to U.S. patent application Ser. No. 07/567,040, which is now U.S. Pat. No. 5,091,280) may be regarded as a most preferred material in which these problems concerning coloring of a non-image portion and low color density were resolved. This recording material is a two component type heat-sensitive recording material in which one of the two components is included in microcapsules and the other component is arranged outside the microcapsules as a hardenable compound of a photo-hardenable composition or together with the photo-hardenable composition.
Also, a recording material for negative image formation developed by employing a similar idea is disclosed in Japanese Patent Application No. 2-19710 (corresponding to U.S. patent application Ser. No. 07/567,040, now U.S. Pat. No. 5,091,280) in which a photopolymerizable composition comprising an electron accepting compound, a polymerizable vinyl monomer and a photopolymerization initiator is arranged outside of microcapsules, and a Layer containing the photopolymerizable composition and the microcapsules, which include an electron donating colorless dye, is coated on a support.
When color recording is attempted using one of these prior art recording materials, a recording material which comprises a plurality of light-sensitive layers each having different sensitive wave length and hue may basically be selected. More preferable multi-color recording materials are disclosed, for instance, in Japanese Patent Application Nos. 1-224930 and 2-19710, such as a multi-color recording medium which comprises a plurality of light-sensitive layers each of them sensitive to different wave length of light and capable of developing different color wherein the color recording medium comprises a layer structure of at least two light-sensitive layers laminated on a support, the layer structure comprising a first light-sensitive layer which is sensitive to light of a central wave length of .lambda.1, an intermediate layer which absorbs light of a central wave length of .lambda.1, a second light-sensitive layer which is sensitive to light of a central wave length of .lambda.2 and develops a different color from the first light-sensitive layer . . . , an intermediate layer which absorbs a light of central wave length of .lambda.i-1 and an i-th light-sensitive layer which is sensitive to a light of central wave length of .lambda.i and develops a different color from the first, second, . . . , and (i-1)-th light-sensitive layers, in that order starting from the side of exposure to light toward the support side of the recording material, the central wave lengths being in the order of .lambda.1&lt;.lambda.2&lt;. . .&lt;.lambda.i where i is an integer of 2 or more.
These prior art light-sensitive heat-sensitive recording materials, however, have the disadvantage of poor resolution due, probably, to the restriction of the size of picture element by the limited particle size of microcapsules to be used, as well as another problem of poor image quality due to light scattering. These problems are important problems to be solved especially when high resolution is required such as in the case of proofs and slides.
With such light-sensitive heat-sensitive recording materials, heat development is carried out at a temperature of from 100.degree. to 200.degree. C. after light-sensitive recording. During the heat development process, a solvent present in microcapsules evaporates and condenses on the inner wall of a heat developing machine which subsequently causes not only staining of the recording material and the developing machine but also the generation of an offensive odor when volatilized into the air around the developing machine. In an extreme condition, the volatilized solvent will even damage the health of persons around the machine.
In addition to these problems, these prior art light-sensitive heat-sensitive recording materials have a tendency to be cloudy or hazy, probably, due to the existence of particles such as microcapsules and emulsified components in their coat layers. Since this type of haze decreases the visibility of images, application of these sensitive materials especially to overhead projection (OHP), slides and the like, which require transmission images, results in a dark and unclear total image due to poor transmission of light due to the haze.
These disadvantages of the prior art materials are fatal especially with a multilayer light-sensitive heat-sensitive color recording material, because the disadvantages in each layer of the recording material are compounded.
As a result, resolution of these problems has been desired in the area especially of color recording materials, not to mention monochrome recording materials.
On the other hand, although these recording materials can be used in many applications, they are generally applied to the formation of reflection images in which images are formed on a white paper support. Since these prior art light-sensitive heat-sensitive recording materials form images by--recording with light, formation of high resolution images could expected. However, a light-sensitive heat-sensitive recording material in which the above-described light-sensitive heat-sensitive layers are formed on a paper support as a typical white support produces uneven images with poor resolution, thus requiring further improvements.
As a means to resolve such unevenness and poor resolution, use of a support laminated with a polyolefin such as polyethylene or polypropylene has been proposed. However, since light-sensitive heat-sensitive recording materials to which the present invention is related require a heat development step, for example, at 120.degree. C. for 5 seconds, the laminated polyethylene or polypropylene cannot tolerate the heat development temperature and therefore its shape begins to change thus resulting in wavy or distorted recording layers.
Another measure to resolve such poor resolution and unevenness involved use of a synthetic paper which is well known in this field. Thus, however, still results in deformation at the time of heat development to such a degree that the recording material cannot be used.
In addition, there is still another problem to be solved in use of a paper support or a laminated paper, that is, formation of fog which occurs when heat development is carried out an extended period of time after the formation of the latent image by exposure.
On the other hand, although these recording materials can be used in many applications, they are generally used in the form of a multi-layer structure involving an overcoat layer, an undercoat layer, an intermediate layer and the like. In this case, layers should be coated onto a support in a multi-layer structure. However, if each of the layers is separately coated one after another, there is disadvantageous in terms of cost and yield.
In the field of silver halide photographic materials, all of coating solutions for layers to be provided are formulated in a gelatin system and they are simultaneously coated onto a support by multi-coating technique utilizing a low-temperature setting property of gelatin. Accordingly, if this technique is employed, simultaneous multi-layer-coating can be conducted in the preparation of the above-mentioned recording materials.
However, if gelatin itself is used as a protective colloid for emulsifying and dispersing a component capable of undergoing color development or achromatization to be microencapsulated, a reactant existing as a capsule wall-forming material (e.g., an isocyanate) rapidly reacts with gelatin at the beginning of the emulsification, whereby flocculation of components occurs and microencapsulation is hardly conducted.
Accordingly, there have been required to attain a microencapsulation technique using gelatin protective colloid.